1. Field of the Invention
The present invention relates generally to a Multiple Input Multiple Output (MIMO) system, and in particular, to a transmit (TX) antenna switching apparatus and method in a MIMO system.
2. Description of the Related Art
Mobile communication systems are normally designed so a plurality of mobile stations (MSs) can communicate with one another via a single base station (BS). When the BS performs a high-speed data transmission to the MSs, a fading phenomenon occurs due to characteristics of radio channels. To overcome the fading phenomenon, a Transmit Antenna Diversity scheme, which is a kind of a multiple antenna scheme, has been proposed.
The Transmit Antenna Diversity scheme transmits signals using plural TX antennas, instead of a single TX antenna, thereby minimizing a loss of TX data due to the fading phenomenon and increasing a data rate. The multiple antenna scheme is classified into a transmit diversity scheme and a spatial multiplexing scheme. The transmit diversity scheme obtains a transmit diversity by transmitting the same data through two TX antennas, and the spatial multiplexing scheme transmits different data through different TX antennas.
A conventional BS has two antennas where one is used as a receive (RX) antenna for a receive diversity gain and the other is used as a TX/RX antenna. In practice, however, a BS normally uses one fixed TX antenna and uses an RX antenna as a dedicated RX diversity antenna.
In this way, when the fixed TX antenna is used, downlink performance is degraded because a channel environment between the fixed TX antenna and the user is different from a channel environment between the RX diversity antenna and the user.